In industries such as consumer electronics, home products and appliances, farming, construction equipment, transportation systems, automotive, aeronautical, and nautical, various manufacturing materials such as aluminum are joined to form relatively lightweight connected parts. Polymeric composites are also being connected to metals or other polymers.
A manufacturer can select materials having favorable characteristics, such as being lightweight, highly-conformable or shapeable, strong, durable, or having a desired texture or color by combining some polymer or composite materials with other materials. An article of manufacture may include various components (e.g., exterior, interior, or decorative features) where materials are selected and configured to withstand, for example, a hot and/or chemically aggressive environment or for painting or chemical resistance over time.
With the increased use of polymers and other low-mass materials, compression molding and post-mold joining techniques, such as laser welding and ultrasonic welding, are also being used more commonly.
Processes for joining similar or dissimilar materials include mechanical joining (e.g., bolts and rivets), fusion joining (e.g., fusion arc welding and laser welding), solid-state joining (e.g., friction-stir welding and ultrasonic welding), brazing and soldering, and adhesive bonding, among others.
Joining materials robustly and without great expense is a challenge. Considerations include chemical, mechanical, and thermal behaviors of materials being joined. When designing a dissimilar-material joint, for instance, factors such as, but not limited to, material thicknesses, surface energy, differences in melting temperature, and thermal expansion/contraction of each material, must be taken into consideration. Differences in material properties of dissimilar materials make weld joining especially challenging and in some cases impossible.
Turning to the figures, and more particularly to the first figure, FIG. 1 illustrates a conventional rivet-joining system 100 in use joining a first workpiece 110 to a second workpiece 120.
The system 100 includes a riveting machine 130 including a body 132 and a piston or punch 134 positioned adjacent and movably with respect to the machine body 132. The system 100 includes a base 140, a die 150, and a rivet 160.
In operation, the machine body 132 is positioned adjacent the first workpiece 110 of the workpieces, as indicated by arrow 133 in FIG. 1.
The rivet 160 is positioned between the punch 134 and the first workpiece 110. The punch 134 pushes down on the rivet 160, as indicated by arrow 180, forcing distal tips 162 of the rivet 160 to pierce the workpieces 110, 120, first through a proximate one 110 of the workpieces 110, 120, beyond an interface 115 between the two workpieces 110, 120, and into a distal one 120 of the workpieces 110, 120.
Designers of conventional techniques have had to choose between more cracks or less rivet flaring, each of which lowers joint quality.
Shortcomings of such techniques include the joint having less strength than desired. Traditional techniques also use relatively short rivets, which do not reach through the lower, second workpiece 120. Joint strength is lower than desired when the rivet 160 is kept to shallow depths and not enabled to flare.
Undesired joint strength can also result from unacceptable levels of cracking (e.g., cracks 117) created in the riveting process. Cracking, including micro-cracks and delamination within the workpieces, is possible especially for workpiece materials having relatively low ductility, such as carbon-fiber thermoplastic composites. To avoid cracking, techniques use relatively short rivets 160 to pierce into the second workpiece 120 as little as possible. Also to avoid cracking, materials having a relatively high ductility are typically used, which limits the options for use in the end product.